• 자원환경지질
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• 제26권4호
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• pp.473-487
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• 1993

The Janggun mine area is occupied by the Proterzoic and the Paleozoic meta-pelites, which are intruded by the Jurassic Chunyang granite. The metamorphic terrain is divided into four zones of progressive metamorphism on the basis of mineral assemblages. The zones are chlorite zone, staurolite zone, andalusite zone, sillimanite zone ascending order. Boundary lines between the zones resemble outline of the Chunyang granite mass. Isograd reactions are chlorite+chloritoid+muscovite=staurolite+biotite+quartz+water, staurolite+chlorite+muscovite+quartz=andalusite+biotite+water, and staurolite+muscovite+quartz=andalusite+biotite+garnet+water between the chlorite zone and the staurolite zone, the staurolite zone and the andalusite zone, and the andalusite zone and the sillimanite zone, repectively. They are univariant reactions in KFMASH component system. Metamorphic conditions estimated from garnet-biotite geothermometers and phase equlibria are $530^{\circ}C$ and lower than 4 kb.

• 대한인간공학회지
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• 제36권5호
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• pp.459-466
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• 2017

Objective: This study examined two traffic signals with a countdown indicator in terms of driver's reaction time and subjective satisfaction score and their performance was compared with a standard traffic signal in driving simulation. Background: Dilemma zone is created when a traffic light changes at intersections. It often pushes drivers to rush in urgent and premature decision making whether to go or stop and thus induces unnecessary mental load among drivers, which may lead to sudden conflicts with following vehicles at intersections. Method: Forty college students (male: 20, female: 20) participated in this driving simulation study. Three traffic signals were employed: (1) standard traffic signal; (2) countdown-separated signal; and (3) countdown-overlaid signal. The countdown-separated and countdown-overlaid signals were designed to inform drivers of the remaining time of a green light before tuning to an amber light. Reaction times (sec) and satisfaction scores (7-point scale) for the two signals with a countdown indicator were compared with those for the standard traffic signal. Results: Reaction times of the countdown-separated (0.49 sec) and countdown-overlaid (0.43 sec) signals were significantly shorter than that of the standard signal (0.67 sec). Satisfaction scores of the countdown-separated (5.3 point) and countdown-overlaid (5.6 point) signals were greater than that of the standard signal (3.8 point). Lastly, the countdown-overlaid signal showed better performance than the countdown-separated signal, but their differences in reaction time (0.06 sec) and satisfaction score (0.3 point) were small. Conclusion: Traffic signals with a countdown indicator can improve drivers' reaction time and satisfaction score than the standard traffic signal. Application: Traffic signals with a countdown indicator will be useful for reducing the length of dilemma zone at intersections, by allowing drivers to predict the remaining time of a green light.

• 대한치과교정학회지
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• 제10권1호
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• pp.7-13
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• 1980

To study some informations on the morphogenesis and developmental process of the coronal suture in rats, the author performed daily oral administrations of demethylchlorotetracycline, a kind of tetracycline group, in the amount of 30mg/kg of body weight to the female rats from the 7th day of pregnancy to the time of delivery. Microscopic evaluation was undertaken on the fetal rats in the experimental group. The subject of this experiment were defined to the fetal rats of each group at 1st, 3rd, 7th and 14th day after birth. All these fetal rats were sacrificed and the heads were removed. All the tissue sections were fixed with $10\%$ formalin, Bouin' and Carnoy' solution and then stained by Hematoxylin-Van Gieson stain, or Feulgen and Rossenbeck, Periodic acid Schiff, and prepared for alcian blue reaction. The results were as follows; 1. The directions of osteogenic fibers were arranged irregulary during first 3 days, but after the 7th day they tended to change radial directions like control group. 2. The density of deep stained cells by Feulgen-Rossenbeck reaction were shown leu in the experimental group than that in the control group in first 3 days, but there was shown no significant difference between both groups after the 7th day. 3. PAS reaction in early stage was generally negative in the experimental group unlike as in the control group, but diffuse reaction was observed in the loose middle zone like as in the control group after 14th day. 4. Alcian blue reaction was negative in cambial zone, and slightly positive in uniting zone compared with control group in early stage. After 14th day, however, there was observed a tendency of moderately positive reaction.

• 한국환경과학회지
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• 제31권1호
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• pp.77-85
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• 2022

Environmental contamination by organic compounds are not only restricted to water, but extends to soil and groundwater as well. However, highly oxidized compounds, such as halogenated organics and nitro-compounds, can be detoxified employing reducing methods. Permeable reactive barrier is one of the representative technologies where zero-valent metals (ZVMs) are employed for groundwater remediation. However, organics contaminates often contaminate the unsaturated zone above the groundwater. Despite the availability of technologies like soil vapor extraction and bioremediation, removing organic compounds from this zone represents several challenges. In this study, the reduction of nitrobenzene to aniline was achieved using zero-valent iron (ZVI) under unsaturated conditions. Results indicated that the water content was an important variable in this reaction. Under dry conditions (water content = 0.2%), the reduction reaction was inhibited; however, when the water content was between 10% and 25% (saturated condition), ZVI can reduce nitrobenzene. Palladized iron (Pd/Fe) can be used to reduce nitrobenzene when the water content is between 2.5% and 10%. The reaction was evaluated over a wide range of temperatures (10 - 40 ℃), and the results indicated that increasing the temperature resulted in increased reaction rates under unsaturated conditions.

• 대한기계학회논문집B
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• 제20권5호
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• pp.1671-1678
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• 1996

In external chemical vapor deposition processes including VAD and OVD the distribution of flame-synthesized silica particles is determined by heat and mass transfer limitations to particle formation. Combustion gas flow velocities are such that the particle diffusion time scale is longer than that of gas flow convection in the zone of particle formation. The consequence of these effects is that the particles formed tend to remain along straight smooth flow stream lines. Silica particles are formed due to oxidation and hydrolysis. In the hydrolysis, the particles are formed in diffuse bands and particle formation thus requires the diffusion of SiCl$\_$4/ toward CH$\_$4//O$\_$2/ combustion zone to react with H$\_$2/O diffusing away from these same zones on the torch face. The conversion kinetics of hydrolysis is fast compared to diffusion and the rate of conversion is thus diffusion-limited. In the language of combustion, the hydrolysis occurs as a Burke-Schumann process. In selected conditions, reaction zone shape and temperature distributions predicted by the Burke-Schumann analysis are introduced and compared with experimental data available. The calculated centerline temperatures inside the reaction zone agree well with the data, but the calculated values outside the reaction zone are a little higher than the data since the analysis does not consider diffusion in the axial direction and mixing of the combustion products with ambient air. The temperatures along the radial direction agree with the data near the centerline, but gradually diverge from the data as the distance is away from the centerline. This is caused by the convection in the radial direction, which is not considered in the analysis. Spatial distribution of silica particles are affected by convection and diffusion, resulting in a Gaussian form in the radial direction.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2977-2983
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• 2008

The combustion characteristics of a partially premixed flame in a dump combustor were studied to determine the effects of hydrogen enrichment in propane. Bluff-body was used for flame stabilization. Fuel mixtures containing a hydrogen mole fraction ranging from 0.1 to 0.5 were burnt at ambient pressure within a quartz chamber. Tests were carried out keeping the total reactant flow rate by adjusting the fuel and air flow rates. The fluctuations of pressure were measured by piezoelectric pressure sensor. The instantaneous flame structure and OH chemiluminescence images were described by High-speed Intensified Charged Coupled Device (HICCD) camera and Intensified Charged Coupled Device (ICCD) camera. The present results show that hydrogen enrichment in fuel changed the location of primary reaction zone from inner recirculation zone to turbulent shear layer and pressure signal. The reason is that chemical aspects take precedence over flow aspects in the hydrogen-enriched flame.

• 대한기계학회논문집B
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• 제23권8호
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• pp.1022-1030
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• 1999

A numerical study was carried out to analyze the effect of flow distribution of stirred part and plug flow part on combustion efficiency at the coal gasification process in an entrained bed coal reactor. The model of computation was based on gas phase eulerian balance equations of mass and momentum. The solid phase was described by lagrangian equations of motion. The $k-{\varepsilon}$ model was used to calculate the turbulence flow and eddy dissipation model was used to describe the gas phase reaction rate. The radiation was solved using a Monte-Carlo method. One-step parallel two reaction model was employed for the devolatilization process of a high volatile bituminous Kideco coal. The computations agreed well with the experiments, but the flame front was closer to the burner than the measured one. The flow distribution of a stirred part and a plug flow part in a reactor was a function of the magnitude of recirculation zone resulted from the swirl. The combustion efficiency was enhanced with decreasing stirred part and the maximum value was found around S=1.2, having the minimum stirred part. The combustion efficiency resulted from not only the flow distribution but also the particle residence time through the hot reaction zone of the stirred part, in particular for the weak swirl without IRZ(internal recirculation zone) and the long lifted flame.

• 대한기계학회논문집
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• 제12권5호
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• pp.1113-1120
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• 1988

본 연구에서는 4종류의 실험 모델을 채택하여 연소 반응용다공성 블럭(combu- stive reacting porous block)내의 화염대 위치와 화염의 온도 분포, 화염이 안정화 되는 범위를 고찰하여 내부 열재순환 효과를 규명하고 예열용 다공성 블럭(preheating porous block)과 복사 차폐용 다공성 블럭(radiative insulating porous block)의 효 과에 대한 연구와 초희박 혼합기나 저 발열량 연료의 연소 가능성을 제시하고 수치 계 산에 필요한 자료를 제시하는 것이다.

• 한국주조공학회지
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• 제25권2호
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• pp.80-87
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• 2005

The microstructure and mechanical property of the Ni and Ni-Cr porous metal reinforced AC4C matrix composites fabricated by squeeze casting were investigated. In this study Ni, Ni-Cr porous metals which are estimated to be easy to fabricate by squeeze casting are used as strengtheners for composite materials. As a matrix material, Al-7wt.%Si-0.3wt.%Mg(AC4C) has been used. In case of Ni/AC4C and Ni-Cr/AC4C composite, $750^{\circ}C$ melt temperature and minimum 25MPa squeezing pressure are needed to produce sound composite materials. The observation of interfacial reaction zone at various heat treatment condition shows that atsolutionizing temperature of above $520^{\circ}C$, the interfacial reaction zone increases proportionally with heat treatment time and the reaction products formed by interfacial reactions are mainly composed by $Al_{3}Ni$ and $Al_{3}Ni_{2}$ phases.

• 공업화학
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• 제18권5호
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• pp.415-423
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• 2007

톱밥 및 왕겨를 주 바이오매스 원으로 선정하여 열분해 특성을 고찰하였다. 열 중량 분석기를 이용하여 승온 속도를 달리하여 질소 분위기의 비등온 조건에서 열분해 분석을 수행하였다. 시료의 열분해 반응은 holocellulose가 주 열분해 대상인 저온 반응 영역과 lignin이 열분해 대상이 되는 고온 반응 영역으로 구분되며 이를 2단계 연속 반응 모델을 사용하여 해석하였다. 각 영역에 따라 1st order reaction model과 3-way transport model을 적용하여 톱밥 및 왕겨의 활성화 에너지를 저온 영역에서 82.5 kJ/mol, 85.1 kJ/mol 그리고 고온 영역에서 19.7 kJ/mol, 22.0 kJ/mol로 결정하였다. 승온 속도를 달리하여 결정된 반응 속도 상수는 Gaur-Reed의 제안 식에 따라 kinetic compensation relation을 통해 해석할 수 있었으며 이를 통해 임의의 승온 속도에서의 열분해 속도 상수를 잘 예측할 수 있었다.